Variable focus optical apparatus

ABSTRACT

A variable focus lens apparatus for use in spectacles or the like is formed from a fluid envelope comprising two sheets, at least one of which is flexible. The flexible sheet is retained in place between two rings, which are directly secured together. This may be by means of adhesive, ultrasonic welding, or any similar process. If the other sheet is rigid, then it may be directly secured to one of the rings.

This is the U.S. national phase of International Application No.PCT/GB02/00022 filed Jan. 2, 2002, the entire disclosure of which isincorporated herein by reference.

The present invention relates to a variable focus optical apparatus, andmore particularly to a variable focus lens suitable for use inspectacles or the like.

Variable focus lenses are known per se, and can take the form of avolume of fluid enclosed flexible transparent sheets. Normally, thereare two such sheets, one forming the front surface of the lens and oneforming the back surface. Both sheets can be flexible, or one can beflexible and one rigid. The sheets are attached to one another at theiredges, either directly or to a carrier between the sheets, to form asealed chamber containing the fluid. Fluid can be introduced into orremoved from the chamber to vary its volume. As the volume of liquidchanges, so the curvature of the sheet(s), and thus the power of thelens, also varies.

Previous variable focus lenses have generally been too heavy and bulkyfor use in spectacles or similar apparatus. A light and compact variablefocus lens is disclosed in WO 98/11458, in which two flexible membranesare tensioned across a first ring, and held in place by engagement ofthe first ring with two other rings. However, the construction of thelens in WO 98/11458 requires that the rings be made from a materialwhich is lightweight, strong and ductile, and this can in practice limitthe range of materials which can be used.

According to the present invention, there is provided a variable focusoptical apparatus, comprising a cavity containing a variable amount oftransparent fluid defined between two transparent sheets, at least oneof said sheets being a flexible membrane which is held in tensionbetween two interengaging rings, wherein the rings are directly securedto each other.

Because the rings are directly secured to each other, there is no needfor them to be formed from a ductile material. Thus, a larger range ofmaterials can be used, which can prove beneficial in terms of cost andweight.

The rings can be secured in any suitable manner. For example, if therings are formed of a plastics material, ultrasonic welding can be used.However, it is preferred that the rings are secured to each other bymeans of adhesive, as this method is of more general suitability.

Preferably, the cavity is defined between one flexible membrane and onerigid sheet, and it is preferred for the rigid sheet to be directlysecured to is at least one of the rings. This simplifies the structureof the lens. It is further preferred for the rigid sheet and the ringsto be secured together by a single application of adhesive, as thismakes the construction of the lens easier.

In an alternative embodiment, the rigid sheet is secured to one side ofone of the rings, and the other ring is secured to the other side of thering. This can be useful if the materials of the rings and the rigidsheet are such that they cannot be secured to each other in a singlestep (for example, because there is no single adhesive which iscompatible with all of the materials used).

Preferred embodiments of the invention will now be described by way ofexample only, and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a part of a known variablefocus lens for use in spectacles or the like;

FIG. 2 is a schematic cross-sectional view of a first embodiment of theapparatus;

FIG. 3 is an enlarged cross-sectional view of the edge of the apparatus;

FIG. 4 is a schematic cross-sectional view of a second embodiment of theapparatus; and

FIG. 5 is an enlarged cross-sectional view of the edge of the apparatus.

As can be seen from FIG. 1, the known lens 100 comprises two flexiblemembranes 102, 104, which are attached to either side of a first ring106. The first ring 106, with the membranes 102, 104 attached, ispositioned inside a second ring 108. A step 110 on the second ring 108engages with a recess 112 on the first ring 106 to hold the lowermembrane 104 taut. Similarly, a step 114 on a third ring 116 is engagedwith a second recess 118 on the first ring 106 to hold the uppermembrane 102 taut. The edge 120 of the second ring 108 is then bent overthe edge of the third ring 116 to hold the rings together as a unit.After the rings have been assembled, a hole can be drilled through themto allow fluid to be introduced into or removed from the space betweenthe membranes 102, 104, in order to vary the focus of the lens.

As the lens 100 is to be used in spectacles or similar vision correctionapparatus, it will be appreciated that it should be made as light aspossible. However, the method of manufacture of the lens requires thatat least the second ring be ductile. Further, as the physical strengthof the lens is derived from that of the rings, these must be strongenough to enable the lens to withstand the kind of accidental damage towhich spectacles and the like are prone. Few materials have the requiredcharacteristics of lightness, ductility and strength, and in practicealuminum or titanium are normally used.

FIG. 2 shows a cross-section of a first preferred embodiment of theoptical apparatus, in the form of a variable focus lens.

The lens 10 comprises first and second rings 12, 14, with the secondring 14 fitting inside the first ring 12. A flexible membrane 16 isretained between the first and second rings 12, 14, and a step 18 on thefirst ring 12 engages with a recess 20 on the second ring 14 to ensurethat the membrane is retained under tension.

However, in contrast to the known lens described above, a rigid sheet 22is used in place of the second flexible membrane. Further, instead ofbeing retained between two rings, the sheet 22 is directly secured tothe rings 12, 14 by means of an adhesive 24. This adhesive also servesto secure the first and second rings together, thus ensuring theintegrity of the lens.

The construction of the lens is as follows:

Firstly, the flexible membrane 16 is positioned inside the first ring12. The second ring 14 is then placed inside the first ring 12 to engagetherewith. Before the step 18 on the first ring 12 enters the recess 20on the second ring 14, it contacts the flexible membrane 16, andfrictionally engages with it. Then, as the step 18 enters into therecess 20, it stretches the membrane 16, putting it under tension. Whenthe step 18 is fully received in the recess 20, the membrane 16 is heldunder tension. The relative heights of the first and second rings aresuch that the first ring 12 projects slightly above the second ring 14when the two are engaged.

Adhesive 24 is then applied to the upper surface of the second ring 14,and the rigid sheet 22 is pressed onto the adhesive 24. The thickness ofthe edge of the rigid sheet 22 is preferably slightly less than thedistance by which the first ring projects above the second, so that itfits into the first ring. However, the thickness can be such that itprojects slightly, if desired. As the sheet 22 is pressed on, some ofthe adhesive 24 is forced sideways to come into contact with the firstring 12. Pressure is maintained until the adhesive has set, to securethe first and second rings 12, 14 and the rigid sheet 22 together as aunit.

A hole is then drilled through the rings to allow the cavity between theflexible membrane and the rigid sheet to filled with transparent fluid.Fluid can be introduced into or removed from the lens through this hole,to enable it to function as a variable focus lens.

Using this method of construction removes the need for any of the ringsto be ductile, although strength and lightness are still factors.Therefore, the range of materials which can be used is larger. Inparticular, certain plastics materials can be used.

The rigid sheet 22 is preferably formed from a plastics material, suchas polycarbonate. It is of course important to ensure that the materialsused to form the rings 12, 14 and the rigid sheet 22 are compatible, andcan be adhered together with an adhesive. As shown in the Figures, thesheet 22 can be curved, but does not necessarily have any appreciableoptical power.

The flexible membrane 16 is preferably formed from Mylar, although otherflexible materials can be used. It has proved extremely difficult toadhere Mylar to other materials using adhesive, and so the flexiblemembrane is retained between the first and second rings, which areadhered to each other, rather than being adhered directly to the rings.

Means other than adhesive can be used to secure the rings together. Forexample, the rings and the rigid sheet can be subjected to ultrasonicwelding.

In the embodiment shown in FIGS. 2 and 3, the second ring 14 and therigid sheet 22 fit inside the first ring 12, and a single adhesion stepis sufficient to hold the lens 10 together. In contrast, in the lens 30of the second embodiment (as shown in FIGS. 4 and 5), the second ringand the rigid sheet are secured separately to the first ring.

As can be best seen from FIG. 5, the first ring 32 has a step 36 and thesecond ring 34 has a recess 38, and the step 36 engages in the recess 38to maintain the flexible membrane 40 under tension, as in the firstembodiment. Adhesive 42 is applied to at least one of the first andsecond rings 32, 34 before they are engaged, and the rings are heldtogether under pressure until the adhesive has set. Adhesive 44 is alsoapplied to one of the first ring 32 and the rigid sheet 46, and theseare also held together under pressure until the adhesive 44 has set.

The assembly of the lens can be carried in two separateadhering-and-pressing steps, one for the second ring 34 and one for therigid sheet 46. Alternatively, the adhesive can be applied to both sidesof the first ring 32, and the second ring 34 and the rigid sheet 46assembled onto the first ring 32 and pressed in a single step. One ormore hollows may be provided on the confronting surfaces of the firstand second rings and the first ring and the rigid sheet, to accommodateexcess adhesive.

Once the lens is assembled, a hole is drilled through it to allow thecavity between the flexible membrane and the rigid sheet to be filledwith transparent fluid, as in the first embodiment.

It will be appreciated that, in reality, there are no gaps between thevarious parts of the lens through which fluid could leak. In theFigures, gaps are shown between the various parts solely to show theconstruction of the lens more clearly.

Further, although various parts of the lenses have been referred to as“rings”, it will be appreciated that they can take the shape of anyclosed curve, and are not necessarily circular. If desired, the rigidsheet can have some cylindrical lens power, to compensate for astigmaticerrors which can be introduced in non-circular lenses.

1. A variable focus optical apparatus, comprising a cavity containing avariable amount of transparent fluid defined between two transparentsheets, at least one of said sheets being a flexible membrane which isheld in tension between two interengaging rings, wherein the rings aredirectly secured to each other.
 2. Apparatus as claimed in claim 1,wherein said rings are secured to each other by means of adhesive. 3.Apparatus as claimed in claim 1, wherein the cavity is defined betweenone flexible membrane and one rigid sheet.
 4. Apparatus as claimed inclaim 3, wherein said rigid sheet is directly secured to at least one ofsaid rings.
 5. Apparatus as claimed in claim 4, wherein said rigid sheetand said rings are secured together by a single application of adhesive.6. Apparatus as claimed in claim 4, wherein said rigid sheet is securedto one side of one of said rings, and the other said ring is secured tothe other side of said one of said rings.
 7. Apparatus as claimed inclaim 2, wherein the cavity is defined between one flexible membrane andone rigid sheet.
 8. Apparatus as claimed in claim 7, wherein said rigidsheet is directly secured to at least one of said rings.
 9. Apparatus asclaimed in claim 8, wherein said rigid sheet and said rings are securedtogether by a single application of adhesive.
 10. Apparatus as claimedin claim 8, wherein said rigid sheet is secured to one side of one ofsaid rings, and the other said ring is secured to the other side of saidone of said rings.